Tablet is a solid dosage form in which powder, crystalline or granular form of drug is compressed in a disk or molded. It is the most frequently used means of administering a drug. The main reasons behind formulation of different types of tablets are to create a delivery system that is relatively simple and inexpensive to manufacture.

Here are tablets classified by their route of administration and by the type of drug delivery system they represent within that route.

1. Oral Tablets for Ingestion: Oral tablet is designed to release the drug within the gastrointestinal tract for absorption into the circulation or more rarely for a local effect. It is usually swallowed or dissolved in water before taking.

These tablets are administered by other route except for the oral cavity and so the drugs are avoided from passing through gastro intestinal tract. These tablets may be inserted into other body cavities or directly placed below the skin to be absorbed into systemic circulation from
the site of application.

Vaginal tablets
This tablet undergoes slow dissolution and drug release in vaginal cavity of women. The shape is kept ovoid or pear shaped to facilitate retention in vagina. The tablet should be made compatible with plastic tube inserters which are designed to place the tablet in the upper region of vaginal tract. These tablets generally release antibacterial, antiseptics or astringents to treat vaginal infections or release steroids for systemic absorption.

These tablets are meant to be swallowed intact along with a sufficient quantity of potable water, except for chewable tablet. Tablet in this category is the most popular world wide and the major attention of the researcher is towards this direction.

Standard Compressed Tablets
These are the standard uncoated tablets, can be made by some methods :

direct compression

wet granulation

dry granulation

double compaction.

They may be used for local action in gastro-intestinal tract or systemic action. When the tablet exert local action, they are formulated as more water insoluble by means of selecting slow dissolving excipients and thus provides local action for long time period, for example antacids and adsorbents.

The drugs that produce systemic action have some aqueous solubility and designed to disintegrate and dissolve quickly so that the drug can be quickly absorbed and produce systemic action.

This dosage form is intended to hydrate and begin to dissolve in duodenum (pH 4 to 6) or in small intestine where pH increases to 7 to 8. The presence of esterases or bile salts like surface active agents plays a role in drug release.

Modified Release tablets
The main purpose of this dosage form is to release the medicament slowly for long time duration after administration of a single tablet.

Matrix technology
Matrix products exhibit first order drug release characteristics. These are the type of controlled drug delivery systems, which release the drug in continuous manner. These release the drug by both dissolution controlled as well as diffusion controlled mechanisms. To control the release of the drugs, which are having different solubility properties, the drug is dispersed in swellable hydrophilic substances, an insoluble matrix of rigid nonswellable hydrophobic materials or plastic materials.

Drug Release from Matrix systems
Drug in the outside layer exposed to the bathing solution is dissolved first and then diffuses out of the matrix. This process continues with the interface between the bathing solution and the solid drug moving toward the interior. It follows that for this system to be diffusion controlled, the rate of dissolution of drug particles within the matrix must be much faster than the diffusion rate of dissolved drug leaving the matrix.

Combination of conventional HPMC matrix technology with upper and lower layer has moderate drug release by increase in surface area with concomitant reduction in drug concentration within the device.

Tablets in this group are release the active ingredient in oral cavity or to provide local action in oral cavity region. The tablets under this category avoids first-pass metabolism, decomposition in gastric environment, nauseatic sensations and gives rapid onset of action.

Lozenges and Troches
The tablet that is intended to produce continuous effect on the mucous membrane of the throat. They are tablets that dissolve slowly in the mouth and so release the drug dissolved in the saliva.
The tablet is a flat faced at least about 18mm in diameter and meant to suck and dissolves in the mouth. The compressed tablet is called troches and the tablets produced by fusion or candy molding process are called lozenges.

Lozenges

Flavours and sweeteners are added to make tablets palatable. The tablet generally contains sucrose or lactose and gelatin solution to impart smooth taste. There is no disintegrating agent. The quality of the binding agent is increased so as to produce slow dissolution. Gum is used to give strength and cohesiveness to the lozenge and facilitating slow release of the active ingredient.

The tablets under this category are required to be dissolved first in water or other solvents before administration or application. This solution may be for ingestion or parenteral application or
for topical use depending upon type of medicament used.

Effervescent tablets
The oral dosage forms are the most popular way of taking medication despite having some disadvantages like slow absorption and thus onset of action is prolong. This can be overcome by administrating the drug in liquid from but, many APIs have limited level of stability in liquid form. So, effervescent tablets acts as an alternative dosage form.

The tablet that contains acid substances and carbonate or hydrogen carbonate that react rapidly in the presence of water to release carbon dioxide. Sodium bicarbonate, citric acid and tartaric acid are added to the active ingredients to make the tablet effervescent. This facilitates tablet disintegration and drug dissolution; the tablet disintegration should be complete within few minutes.

Almost all dyes used in medicine is a synthetic dye. Only a few are using natural dyes. These dyes used to color tablets (coated and uncoated), staining on the shell capsules, and syrup coloring. Giving color to the drug in addition to the aesthetic factor is also intended as product identification.

Tablet
Tablets coloring made using the tablet coating technology, especially the coating film. Film coating on tablets aims to:

aesthetic tablets

maintaining the stability of tablets

product identification.

Drug that color does not attract as herbal extracts, color cloudy, dull and uneven can be covered. There are two kind of dyes used in film coatings:

Not all drugs need to be coated. There are still shows its original color form, or given at the time prior to printing color tablets, mixing both dry and wet granulation.

Capsule
There are two forms of capsule, hard-shelled capsule and soft capsule. Hard capsules consisting of body and cap while soft capsule is a unity. The dye in the capsule particularly hard-shelled capsule serves to know the identity of the pharmaceutical industry.

Hard capsules may also contain dyes that are allowed or dyes from a variety of iron oxide, opaque material such as titanium dioxide, dispersing materials, hardening materials such as sucrose and preservatives. Usually this material contains between 10-15% water.

A pigment is a material that changes the color of reflected or transmitted light as the result of wavelength-selective absorption. This physical process differs from fluorescence, phosphorescence, and other forms of luminescence, in which a material emits light.

A dye is a colored substance that has an affinity to the substrate to which it is being applied. The dye is generally applied in an aqueous solution, and may require a mordant to improve the fastness of the dye on the fiber.

Points of Difference

Dyes

Pigments

Solubility

Soluble in water

nsoluble in water and most of the solvents

Number

Available in Large number

Comparatively lesser in number

Product resistance

Lower as compared to pigments

Very high

Lightfastness

Lower Dyes are very much vulnerable. Lights destroy colored objects by breaking open electronic bonding within the molecule

Compatibility with gelatinAldehydes. Incompatibilities are known to occur; with certain substances that contain reactive aldehydes. The aldehydes can react with the gelatin by forming crosslinks.

Cross-linking is not inevitable, but depends on several mechanisms. The main contributory factors are storage stress (high temperature, high humidity, excessive light exposure) and the presence of aldehydes, for example formaldehyde.

Water Content and Humidity. Incompatibility also occurs caused by the water content of the gelatin shell. If a substance is highly hygroscopic, it might absorb water from the capsule shell. This process can lead to brittleness of the shell, which might break under mechanical strain. If the drug substance in the capsule is sensitive to humidity the water content of the shell, which is normally between 13% and 16%, can lead to the degradation of the drug substances.

Hygroscopic compounds
Hygroscopic compounds can absorb water out of the shell, which normally has a water content of 13% to 16%. This can subsequently lead to brittleness and drying out of the shell.
The absorption of moisture during production can lead to the build up of a sorption film that affects the fluidity of the powder mix filling. Ideally, hygroscopic compounds should be combined with the diluent mannitol as mannitol is relatively inert where water absorption is concerned.

Adhesion
Adhesion of many drug actives or excipients might lead to difficulties during capsule filling, as particles stick to the surfaces of the filling machine. The consequences is that the fill substance breaks up, which leads to unacceptable fill variations. To overcome this problem, It is advisable to add a glidant or a combination of a glidant and lubricant such as Aerosil, magnesium stearate, or talcum/stearic acid.

Hard gelatin capsule are actually easier and quicker to formulate and produce, whatever the batch size, compared with other solid oral dosage forms. Indeed, by using hard gelatin capsules it is possible to produce small or very small batch sizes on manual or semi-automatic filling machine.

Hard gelatin capsules usually require between one and four excipients. In fact there is drug in capsule form that contains only the active ingredient, which means there is no excipient.

Some excipients might have several functions. Talcum, for instance, serves as a lubricant in concentrations below 5%. At higher concentrations, it is mainly considered as filler. Microcrystalline cellulose also serves as a disintegrant besides filler.

The functions of excipients in hard gelatin capsules can be different their functions in tablets. Starch, which is commonly added to tablets as a disintegrant owing to its macerating properties of 5% to 10%, might be used as a filler in hard gelatin capsules because the macerating properties are not strong enough to really disintegrate the lightly compressed substances in hard gelatin capsules.

1. Neutralization
Neutralization phase will eliminate a large amount of free fatty acids contained in oil. This will increase the smoke point, flash point and fire point. So, when margarine used for frying will not be easily oxidized to form acrolelin undesirable because it can cause itching in the throat.

Fat would be flammable, if there is lot of free acid. This is because since the critical parameters of temperature (smoke point, flash point & fire point) lower. Therefore, the fat needs to be purified with the neutralization process.

Smoke point: the temperature where the first occurrence of thin bluish smoke when heated fat.

Flash point: the temperature where the fat starts to burn when the heating continued.

Fire point: temperature where the fat burned steadily.

Neutralization is the process of separation of free fatty acids from oils or fats by reacting the free fatty acid with a base or other reagents to form soap (soap stock). Neutralization in the scale industry generally use NaOH because it is more efficient and cheaper than any other neutralization.

Excellence neutralization using NaOH:
• reduce the dye and dirt in the oil
• be able to remove phosphatides, proteins, resins and suspension in the oil that cannot be removed by gum separation processes.

The more dilute solution of NaOH used, the smaller neutralized but will more likely the loss of oil because the oil with soap to form an emulsion. Generally, free fatty acids containing a lower concentration used 0.15 N. NaOH.

Soap is formed in this reaction can help the separation of impurities such as dyes and phospholida and proteins by forming an emulsion. Penetration will also neutralized a small amount of neutral oil (trigleserida, monogleserida, diglycerides and triglycerides). By centrifugation, soap or emulsion formed can be separated from the oil.